Update {virtual,override} to follow C++11 style in cloud_print.

cloud_print/gcp20/prototype/cloud_print_xmpp_listener.h

Index: cloud_print/gcp20/prototype/cloud_print_xmpp_listener.h
diff --git a/cloud_print/gcp20/prototype/cloud_print_xmpp_listener.h b/cloud_print/gcp20/prototype/cloud_print_xmpp_listener.h
index 32dde8c1a289e9cad074a20ffd862c7064249683..8c8ed9d0df0b93ad49bd303f56d7e1618b411a79 100644
--- a/cloud_print/gcp20/prototype/cloud_print_xmpp_listener.h
+++ b/cloud_print/gcp20/prototype/cloud_print_xmpp_listener.h
@@ -65,7 +65,7 @@ class CloudPrintXmppListener
       scoped_refptr<base::SingleThreadTaskRunner> task_runner,
       Delegate* delegate);
 
-  virtual ~CloudPrintXmppListener();
+  ~CloudPrintXmppListener() override;
 
   // Connects to the server.
   void Connect(const std::string& access_token);
@@ -75,12 +75,12 @@ class CloudPrintXmppListener
 
  private:
   // notifier::PushClientObserver methods:
-  virtual void OnNotificationsEnabled() override;
-  virtual void OnNotificationsDisabled(
+  void OnNotificationsEnabled() override;
+  void OnNotificationsDisabled(
       notifier::NotificationsDisabledReason reason) override;
-  virtual void OnIncomingNotification(
+  void OnIncomingNotification(
       const notifier::Notification& notification) override;
-  virtual void OnPingResponse() override;
+  void OnPingResponse() override;
 
   // Stops listening and sending pings.
   void Disconnect();